Unsaturated resin compositions typically have used styrene monomers, like styrene as a reactive diluent, to adjust and reduce the viscosity of the resin compositions, generally in amount of up to 50% by weight, e.g., 5 to 40%. The unsaturated resin compositions include unsaturated polyester resin compositions prepared by the reaction of unsaturated acids with alcohols, such as dicarboxylic acids and dihydroxy alcohols.
Ethylenic unsaturation is usually realized by the use of maleic and fumaric acids or anhydrides; however, such compositions may also contain saturated acids, like phthalic and adipic acids to adjust resin properties. The dihydroxy alcohols used in the preparation may include: ethylene; propylene; diethylene; dipropylene glycols; and neopentyl glycol. These resin compositions contain cross-linking agents, like styrene and diallyl phthalate, and are peroxide curable to provide thermosetting resins.
The vinyl ester resin compositions comprise the vinyl esters of various acids, typically, short chain aliphatic and dicyclic acids, like C2-C6 acids, such as acetic acid. These vinyl ester resin compositions, such as polyvinyl acetate, contain cross-linking agents and styrene monomers and are subject to peroxide cure to produce a thermosetting vinyl ester resin.
While the use of styrene monomers provides a satisfactory product, the Environmental Protection Agency (EPA) requires that such cross-linkable resin compositions meet EPA regulations for volatile organic compounds (VOC).
The search for styrene monomer substitutes to meet VOC regulations is directed to low VOC compounds which are not flammable. Such substitutes are usually limited to: acrylic monomers; oligomers; methyl methacrylates; and allyl alcohol ethers. However, the acrylic monomers are usually associated with strong odor, low viscosity, strong skin irritation, and slow peroxide cure.
Acrylic oligomers are typically too high in viscosity and do not lend themselves to reduction in viscosity like the styrene monomers do. The allyl alcohol compounds tend to be very slow curing, and like the acrylics, are inhibited by air to cure with peroxides. Further, methyl methacrylate monomers are classified, like styrene monomers, by the EPA and have a strong objectionable odor.
It is desirable to provide a substitute for styrene monomers in resin compositions, which substitute provides a reactive diluent which overcomes the prior objections of other proposed prior art substitutes.
The invention relates to methyl methacrylate-urethane oligomers, the method of preparation of the same, polymers produced therefrom, and resin compositions wherein the oligomers are employed in whole or in part as styrene monomer substitutes.
The invention comprises a low viscosity methyl methacrylic-urethane oligomer prepared by the reaction of a hydroxyalkyl methacrylate monomer with an elastomeric urethane prepolymer having free NCO groups, and the oligomer is typically characterized by a viscosity of less than about 500 centipoise (cP).
The invention relates to a polymer prepared by the polymerization of the oligomer, typically by peroxide cure, free radical cure, or radiation cure of the oligomer alone or with other monomers or oligomers. The invention also comprises a low viscosity alkyl methacrylic-urethane oligomer prepared by the reaction of and in the presence of a catalyst of a hydroxyl ethyl or hydroxyl propyl methacrylate monomer with a flexible elastomeric urethane prepolymer, and generally having about 5 to 15% free NCO groups in about a stoichiometric amount or very minor excess of 0.1 to 0.2%, or in an excess of the methacrylate monomer, such as up to about 2 to 5 percent.
While the oligomer may be prepared with an excess of free NCO groups, the reaction preparation is not preferred, since the free NCO groups in the oligomer tend to react with moisture in the air and to cause foaming of the oligomer. The preferred reaction is to employ a stoichiometric amount or a slight excess of the methyl methacrylate monomer.
The resin composition, with the oligomer, may include: stabilizers; catalysts; promoters; curing agents; various filler materials; and other additives and components used in and with oligomers and resin compositions to prepare oligomer resin compositions suitable for use as: paint coatings; industrial floor coatings; gel coat replacement in laminates, such as rigid urethane foam-polyester composite laminate structures; marble coatings; and/or other industrial applications.
It has been discovered that the oligomers of the invention are characterized by low viscosity, such as less than 500 cP at 25xc2x0 C., and preferably, less than 200 cP, e.g., about 100 cP and are suitable as styrene monomer substitutes in resin compositions, without sacrifice time or properties, and most important, the oligomers reduce VOC""s to lower and acceptable levels.
The oligomers may be used in whole or in part as styrene monomer substitutes and may be used alone or with styrene monomers or other polymerizable monomers.
The oligomers, particularly those aliphatic or alicyclic urethane oligomers, may be used to produce UV stable coatings and polymers without VOC""s for a number of novel and useful applications.
The hydroxyalkyl methacrylates employed are preferably: hydroxyethyl methacrylate (HEMA); hydroxypropyl methacrylate (HPMA); or mixtures thereof. The hydroxymethyl methacrylate (HEMA), when used by itself, produces a brittle polymer which can still be a skin irritant, and HEMA is also quite sensitive to air inhibition.
The oligomers of the invention are low viscosity oligomers and may be employed as a reactive diluent, i.e., as a styrene or methyl methacrylate monomer substitute with unsaturated resin compositions, generally peroxide-curable resin compositions in amounts of 5 to 90% by weight, such as about 10 to 30% by weight.
The oligomers are prepared generally in the presence of a catalyst, and optionally but preferably, in the presence of a promoter to provide the methyl methacrylate urethane oligomers. The catalyst and promoter materials and amounts used may vary but organo-metallic catalyst, such a tin salts as a catalyst, and cobalt salts, like DMAA and DMA and various amines as promoters are satisfactory.
The reactants are mixed and heated, e.g., 120 to 180xc2x0 F., for a time of about 2 to 8 hours. The reactants may be used in varying amounts, but generally in about stoichiometric amounts. It is desirable to add a stabilizer or inhibitor to the reaction mixture to stabilize and prevent premature polymerization of the resulting oligomer, such as quinones and hydroquinones and derivatives.
The oligomers are cross-linkable with other monomers, such as in the resin composition or by itself, by the use of organic peroxides and promoters, like methyl ethyl ketone peroxide (MEKP), benzyl peroxide with amine promoters, like dimethylamine (DMA), diethylamine, and diethanolamine (DEA).
The solution and preparation of the elastomeric urethane prepolymer is important, due to the normal brittle nature of the methyl methacrylate monomers used in the reaction. The urethane prepolymer should be an elastomeric flexible prepolymer with free NCO groups for reaction with the selected amount of the methyl methacrylate monomer, generally greater than 50% by weight of the methyl methacrylate, e.g., 70 to 80% by weight with a prepolymer of 8 to 12% free NCO groups.
The elastomeric urethane prepolymers may be prepared with aromatic, aliphatic, or alicyclic polyisocyanates, typically diisocyanates reacted with polyols or amines which produce elastomeric urethanes.
Elastomeric urethane prepolymers, with about 10% free NCO for the best results, may be prepared employing primary linear diols and triols to include ethylene:oxide capped diols and triols, as well as linear polyesters and polyesters with free hydroxyl groups and aliphatic amines. Suitable polyisocyanates to prepare the prepolymers include: NCO uretedimine MDI; aliphatic dimer NCO; and isophorone diisocyante. Aliphatic urethane oligomers of low viscosity, e.g., 100 to 500 cP, are prepared from aliphatic diisocyanates and aliphatic amines of about 2000 MW and 5 to 10 NCO groups with HEM or HPMA in the presence of a tin catalyst and inhibitor.
The oligomer and oligomer resin composition may contain varying amounts of filler material, such as, but not limited to 5 to 50% by weight of: glass fibers; stone dust; calcium carbonate; metal oxides; and flame retardants, like aluminum trihydrites to provide marble-simulated resin coatings.
The oligomer of the invention may be schematically represented generally by the formula: 
wherein R is an alkyl radical, such as C2-C4, such as a ethyl or propyl, the oligomer having a molecular weight of less than about 5000 and greater than 1200.